This invention relates to a method of treating heparin preparations to isolate a heparin fraction having improved anticoagulant activity and to the improved preparation.
Heparin is a mucopolysaccharide composed of amino sugar and uronic acid residues which is obtained from beef, porcine, sheep, whale, or other mammalian tissue by extraction with a solution of potassium acetate, alkaline ammonium sulfate and the like. Commercial heparin preparations are now widely available from many U.S. drug companies and are distributed primarily for use as intravascular anticoagulants. Recently, heparin has been used clinically as a therapeutic agent for preventing intravascular emboli formation which commonly result in pulmonary embolism and stroke.
Heparin preparations are known to be heterogeneous on a molecular level. Thus, they exhibit a considerable degree of polydispersity in molecular size, variations in the ratio of glucuronic acid to iduronic acid, alterations in the amount of ester and N-sulfation, and differing extents of N-acetylation. Changes in any of these parameters have been correlated only to a very limited extent with heparin's anticoagulant potency. Accordingly, it has been widely assumed that its anticoagulant activity is not traceable to a single specific heparin structure, and in any event, no precise relationship between its structure and function has been forthcoming.
A heparin fractionation technique has now been reported that is based upon the avidity of the complex carbohydrate for antithrombin. See U.S. Pat. No. 4,301,153 to Robert D. Rosenberg entitled "Heparin Preparation", and "Anticoagulant Activity of Heparin: Separation of High Activity and Low-Activity Heparin Species by Affinity Chromatography on Immobilized Antithrombin", FEBS. LETTERS, Vol. 66, No. 1, pp 90-93 (July 1976), the teachings of which are incorporated herein by reference. Both procedures utilize antithrombin bound to a sepharose matrix to isolate anticoagulantly active mucopolysaccharide.